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<p>This study compares electron dynamics in the Van Allen belts and the slot region during two major geomagnetic storms: the Halloween storm (October–November 2003, disturbance storm time index Dst = -383 nT), driven by successive interplanetary coronal mass ejections (ICMEs), and the 10–11 May 2024 storm (Dst = -412 nT), caused by a composite ICME formed by interacting coronal mass ejections. I n the slot region (L = 2–3), the flux enhancement during the main phase of the 2024 storm was very limited (median During/Before ratios: 3.0 at 0.55&#xa0;MeV, 1.9 at 0.65&#xa0;MeV, 2.4 at 1.70&#xa0;MeV), in clear contrast to the Halloween storm’s large immediate increases (136.7 at 3.75&#xa0;MeV, 31.3 at 8.25&#xa0;MeV). However, the 2024 event exhibited a remarkable delayed amplification, with median After/Before ratios of 1681, 693, and 317, and After/During ratios exceeding 500, compared to ~ 10–12 in 2003. This result demonstrates that the final slot state depends more on post-storm acceleration efficiency, via very low frequency (VLF) chorus waves, ultra-low frequency (ULF)-driven radial diffusion, and substorm injections, than on storm intensity alone. Post-peak exponential decay fits yield systematically shorter lifetimes that are energy-dependent. In 2024, τ = 3.83 ± 0.26 d at 0.55&#xa0;MeV, 3.82 ± 0.23 d at 0.65&#xa0;MeV, and 11.77 ± 0.98 d at 1.70&#xa0;MeV. For the November 2003 recovery, τ = 8.34 ± 0.78 d (3.75&#xa0;MeV) and 8.20 ± 1.26 d (8.25&#xa0;MeV); during the later December phase, the timescales diverge sharply, with τ = 3.13 ± 0.10 d at 3.75&#xa0;MeV versus 18.77 ± 1.90 d at 8.25&#xa0;MeV. All fits show good to excellent correlations (R ≥ 0.882), confirming that pure exponential loss dominates once the acceleration ceases. The loss timescales increase with energy, consistent with pitch-angle scattering by plasmaspheric hiss, and the strong divergence in the December 2003 period reveals a pronounced energy filtering effect. Overall, extreme storms can produce significant delayed enhancements when the interplanetary driver sustains wave activity and injections, even with a weak prompt injection. These findings provide valuable new insights for radiation risk forecasting for satellites in medium-Earth orbit (MEO), geostationary Earth orbit (GEO), and low-Earth orbit (LEO). </p>

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Analysis of particle flux variations in the radiation belts during the intense geomagnetic storms of October–November 2003 and 10–11 May 2024

  • 期刊论文

  • 发表日期：

    2026年6月17日

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  • Younoussa Diakite,
  • Christian Zoundi,
  • Yacouba Sawadogo,
  • Jean Louis Zerbo

摘要

This study compares electron dynamics in the Van Allen belts and the slot region during two major geomagnetic storms: the Halloween storm (October–November 2003, disturbance storm time index Dst = -383 nT), driven by successive interplanetary coronal mass ejections (ICMEs), and the 10–11 May 2024 storm (Dst = -412 nT), caused by a composite ICME formed by interacting coronal mass ejections. I n the slot region (L = 2–3), the flux enhancement during the main phase of the 2024 storm was very limited (median During/Before ratios: 3.0 at 0.55 MeV, 1.9 at 0.65 MeV, 2.4 at 1.70 MeV), in clear contrast to the Halloween storm’s large immediate increases (136.7 at 3.75 MeV, 31.3 at 8.25 MeV). However, the 2024 event exhibited a remarkable delayed amplification, with median After/Before ratios of 1681, 693, and 317, and After/During ratios exceeding 500, compared to ~ 10–12 in 2003. This result demonstrates that the final slot state depends more on post-storm acceleration efficiency, via very low frequency (VLF) chorus waves, ultra-low frequency (ULF)-driven radial diffusion, and substorm injections, than on storm intensity alone. Post-peak exponential decay fits yield systematically shorter lifetimes that are energy-dependent. In 2024, τ = 3.83 ± 0.26 d at 0.55 MeV, 3.82 ± 0.23 d at 0.65 MeV, and 11.77 ± 0.98 d at 1.70 MeV. For the November 2003 recovery, τ = 8.34 ± 0.78 d (3.75 MeV) and 8.20 ± 1.26 d (8.25 MeV); during the later December phase, the timescales diverge sharply, with τ = 3.13 ± 0.10 d at 3.75 MeV versus 18.77 ± 1.90 d at 8.25 MeV. All fits show good to excellent correlations (R ≥ 0.882), confirming that pure exponential loss dominates once the acceleration ceases. The loss timescales increase with energy, consistent with pitch-angle scattering by plasmaspheric hiss, and the strong divergence in the December 2003 period reveals a pronounced energy filtering effect. Overall, extreme storms can produce significant delayed enhancements when the interplanetary driver sustains wave activity and injections, even with a weak prompt injection. These findings provide valuable new insights for radiation risk forecasting for satellites in medium-Earth orbit (MEO), geostationary Earth orbit (GEO), and low-Earth orbit (LEO).